This invention relates to valve assemblies, and more particularly to self-contained, captured valve assemblies.
Generally, all valve assemblies comprise a valve housing, having one portal exposed to the combustible fluid, and a valve stem, mounted within the housing and either in contact with the housing or a gasket material. The valve stem is movable from a closed position, preventing flow of the combustible fluid to an open position allowing the combustible material to pass through the valve stem.
Valve assemblies can generally be classified as either "captured" and "self-contained" or "uncaptured". The captured valve assemblies comprise a closed unit with the valve stem, valve housing, gasket material, if used, and biasing member enclosed therein by a bushing member so as to form a single unitary product. The uncaptured valve assemblies eliminate the bushing member and have each component separate, requiring a final assembly and an external member to bias the valve stem in the closed position.
The major difference between captured valve assemblies and uncaptured valve assemblies is the cost of manufacturing. In the captured, or self-contained, valve assembly, the biasing member, which is generally a spring, is mounted directly within the valve assembly under compression between the valve stem and the bushing member, in a manner which biases the valve stem into the closed position with the valve housing. In order to produce a valve stem which will accommodate the captured spring and allow the valve stem to be biasingly engaged with the valve housing, and slidably through the bushing member without leakage, the valve stem must be separately machined. As a result, the valve stem is an expensive item to manufacture. Consequently, the captured or self-contained valve assembly, although preferable in most applications since assembly is complete, is a more expensive valve assembly, due to the labor involved and the cost of manufacturing.
In the uncaptured valve assembly, the valve stem may be die-cast, since its construction is relatively simple compared to the captured valve stem. As a result, the uncaptured valve assembly is much less expensive than the captured valve assembly, but requires additional labor in its final assembly, as well as additional parts handling problems. Also, the uncaptured valve assembly requires an external biasing member to move the valve stem from a closed position to an open position and also to bias the valve stem in the closed position when combustible fluid flow is not desired.
Another problem found with prior art valve assemblies is the inherent cost necessitated by the requirement of machined housings. Since the base of the housing is in direct contact with the combustible fluid, a machined housing is needed to prevent leakage. If a die cast housing were employed, the porosity of the die cast housing would allow leakage of the combustible fluid through its walls to the atmosphere. This would cause a loss of fluid, as well as secondary ignition.
An additional problem found in uncaptured valve assemblies is leakage of the combustible fluid between the valve stem and the valve housing, which results in loss of fluid and can produce secondary ignition when the valve stem is in the open position. Secondary ignition is extremely undesirable since it can cause deterioration of the external member controlling the valve stem.
It is a principal object of this invention to provide a captured or self-contained valve assembly that is easy and inexpensive to manufacture and competitive with the cost of uncaptured valve assemblies.
Another object of this invention is to provide a captured or self-contained valve assembly of the above character which eliminates secondary ignition.
Another object of this invention is to provide a captured or self-contained valve assembly of the above character employing a die-cast or molded valve stem.
A further object of this invention is to provide a captured or self-contained valve assembly of the above character wherein O-ring seals are eliminated and the potential leaking zone are efficiently and completely sealed with an inexpensive flexible sealing system.
Other and more specific objects will in part be obvious and will in part appear hereinafter.
A further problem found in prior art value assemblies is the need for O-rings. O-rings are generally employed for sealing the area between the valve housing and the case in which the housing is mounted. The O-rings, however, suffer from two troublesome problems--cost and flash. O-rings have become expensive items and increase the cost of the valve assembly. Also, since O-rings are molded products, they incorporate flash about their periphery which produces gaps in the sealing area and allows leakage of the combustible fluid.